1. Technical Field
The present invention related to an evaporated gas supply method in which an evaporated gas having a primary pressure filled in a cylinder is reduced in pressure to a secondary pressure through adiabatic expansion, and the evaporated gas having the secondary pressure is supplied to a predetermined consuming installation.
2. Prior Art
For the purpose of realizing a long-term supply of an evaporated gas in a case where the evaporated gas is supplied to a semiconductor manufacturing factory, such a conventional evaporated gas supply system has been used that the said evaporated gas is filled at a high-pressure condition (for example, 52 kg/cm.sup.2.abs) in a cabinet cylinder, and it will be supplied after its pressure is reduced by an expansion valve.
Referring to FIG. 10 and FIG. 11, the evaporated gas supply system of the prior art will be described. FIG. 10 is a view showing the outline of a conventional evaporation and supply apparatus and FIG. 11 is a graph showing a change of pressure in an expansion valve.
In a cabinet cylinder 1, an evaporated gas 2 is filled at a high-pressure (primary pressure) condition. A pipe 4 is laid from this cabinet cylinder 1 to a consuming installation 3 such as a semiconductor manufacturing factory, and an expansion valve 5 is attached on the way thereof. By means of this expansion valve 5, the evaporated gas 2 in the cabinet cylinder 1 is reduced in pressure so as to provide the evaporated gas 2 having a low pressure (secondary pressure) usable in the consuming installation 3.
According to the evaporated gas supply method of the prior art, the evaporated gas 2 is being preserved in the cabinet cylinder 1 for a long period of time, and therefore, the evaporated gas 2 to be supplied gets in a saturated state or a state near thereto. If the evaporated gas 2 is supplied from such state by way of the expansion valve 5, a liquid seal will be caused to take place. For instance, in a case where 100% N.sub.2 O having a primary pressure of 50 kg/cm.sup.2 is led to the expansion valve 5 so that its pressure is reduced to a secondary pressure of 5 kg/cm.sup.2, it will become N.sub.2 O comprising 97% of gas and 3% of liquid. As a result, a liquid seal takes place, resulting in such a problem that the same evaporated gas 2 can not be supplied at a predetermined flow rate to the concuming installation 3.
It is an object of the presnt invention to provide an evaporated gas supply method in which the liquid seal of an evaporated gas can be prevented from taking place.